As temperature is applied to a material when a component is traveling through a cure oven, usually to cure an electrodeposition coating or electrostatic paint, the material will expand at a rate proportional the change in temperature. Different materials have different rates at which they expand. If the difference in thermal expansion is great enough between two bonded dissimilar materials, such as steel and aluminum, deformation can occur in either the joined materials or the mechanical joint.
When adhesive is applied to these joints, the thermal expansion difference may also cause failure of the adhesive before it can fully cure to both surfaces. To account for this, adhesive suppliers have formulated adhesives to maintain flexibility during the curing process to account for this thermal expansion difference without failing. The challenge for the adhesive is to maintain enough flexibility to prevent failure when there is thermal expansion difference between the bonded surface, but then to maintain long term durability after cure. Typically increasing flexibility of the adhesive will compromise the shear strength.